One of the most common health problems and one of the most debilitating is lower back pain. As a result there have been developed exercises specially designed for persons with such afflictions. Unfortunately, most of these cannot effectively exercise the most critical muscle groups in the lower spinal region, namely, the muscles running vertically along each side of the spine. Water has been recognized as a valuable medium in which to carry out therapeutic exercises. The conventional horizontal "dolphin type" flippers have been used in such remedial exercise programs to exercise muscles in the lower back and legs. However, such exercise programs are not only ineffective to relieve lower back pain but may actually lead to increased levels of such pain.
Other types of aquatic devices designed to provide remedial exercise rather than simply enhance swimming are not optimized to exercise the deep set muscles in the lower back. Some swim fins which function differently than "dolphin type" flippers include that disclosed in U.S. Pat. No. 3,521,312 issued to Ganev. Ganev discloses a swim fin having a shoe and a fin extending from the base of the shoe perpendicular to the sole surface. Although Ganev does not disclose using the swim fin for exercising, it does disclose a structure that would increase resistance to sideways movement of the legs. However, the shape of the Ganev fin provides a symmetrical gradually increasing area extending downwardly from the center of the sole of the foot of the user. With such a configuration the efficiency of transfer of force to the water is relatively small as the effective center of area of the fin is relatively far from the user's foot.
Volker, in U.S. Pat. No. 1,590,484, discloses a fin which has an area distribution closer to the user's foot but which extends downwardly and to one side so that it transfers momentum to the water much more effectively in one direction than the other. The Volker fin is specifically designed for enhancing a swimmer's performance of the breast stroke.
Accordingly, it is an object of the invention to provide an improved aquatic device for exercising the lower back and upper legs.